Safety device for preventing the excessive speed of water turbines

ABSTRACT

A safety-valve for preventing the overspeed of an hydraulicturbine runner has passages communicating between the servocontrol valve and the servomotor which varies the position of the pivotal vanes of the runner. The safety-valve member leaves the passages unobstructed in its normal position and is hydraulically biased into this position by a substantially constant pressure which is relieved upon the development of overspeed and a slight displacement of the valve member under the hydraulic pressure resulting therefrom to substantially instantaneously drive the valve member into an opposite position in which the flow paths are blocked and fluid displacement to or from the servomotor is made independent of the control valve and such that the blades pivot into an open position.

United States Patent [1 1 V I I Rakcevlc SAFETY DEVICE FOR PREVENTINGTHE EXCESSIVE SPEED OF WATER TURBINES [75] Inventor: Savo Rakeevi,Ljubljana,

Yugoslavia [73] Assignee: Titovi Zovodi Litostroj, Ljubljana,

Yugoslavia 22 Filed: 0ct.l0,1972 211 App]. No.: 296,089

Almqvist 416/157 [4 June 28, 1974 Primary Examiner-Everette A. Powell,Jr. Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno ABSTRACT Asafety-valve for preventing theoverspeed of an hydrauhc-turbine runnerhas passages communicafifi g between the servo-control valve and theservomotor which varies the position of the pivotal vanes of the runner.The safety-valve member leaves the passages unobstructed in its normalposition and is hydraulically biased into this position by asubstantially constant pressure which is relieved upon the developmentof overspeed and a slight displacement of the valve member under thehydraulic pressure resulting therefrom to substantially instantaneouslydrive the valve member into an opposite position in which the flow pathsare blocked and fluid displacement to or from the servomotor is madeindependent of the control valve and such that the blades pivot into anopen position.

4 Claims, 2 Drawing Figures PATENTEDJUN28 9M SL820 917 SHEET 1 OF 2PATENTED JUH 28 1974 3320.917

SHEET 2 OF 2 The present invention relates to a safety device forpreventing the excessive speed of water turbines.

Water turbines, particularly Kaplan turbines, can attain onoverspeeding, rotational speeds of three times greater than their ratedspeeds. The rotating parts, e.g., the turbine runner and the rotor ofthe alternator are loaded by forces which increase approximately withthe square of the speed. In designing Kaplan turbines and correspondingaltemators, particularly with great units, complicated problems thusarise.

For reducing the rotational speed and the duration of operation at thismaximum speed, various devices are used, such as weirs placed before orbehind the turbine, special oil pressure devices for closing the turbineguide wheel, special servomotors allotted to single vanes of the turbineguide wheel, and the like.

All these solutions have the common imperfection that it is difficult,due to great flows of water, to reduce the operational speed of theturbine by weirs. When the weir is placed behind the turbine in thesuction pipe it has a smaller size than when it is placed before theturbine, nevertheless its closing speed is limited due to thecomparatively big weir and to unfavourable dynamic events in thedischarge system of the turbine, and this is the reason why in such amanner the rate of overspeeding revolutions cannot be-substantiallyreduced. Practically, only a reduction of the duration of turbineoperation at maximum speed can be obtained by the weirs.

Additional pressure devices can fulfil thei task only when thecontrolling organs and the installations from the turbine to the valvewhich isolate the pressure device from the turbine governor are in goodorder. Moreover, such devices complicate the system of control,protection and automation.

The embodiment with separate servomotors for each vane of the turbineguide wheel has failed because of unfavorable dynamic phenomenaoccurring when the vanes are not closed synchronously andthe flowthrough the turbine runner becomes nonuniform during closing.

Attempts have been made to improve the reliability of closing theturbine guide wheel by designing guide vanes for self-closing. In thiscase, of course, servomotors are necessary on each guide vane in orderto remove friction in the governing mechanism of usual design. In thiscase, the servomotors are hydraulically synchronized. This solution hasthe disadvantage that a great number of connections is needed, wherebythe reliability of the arrangement is reduced and is influenced also byfaults in the system for hydraulic synchronization. Thereforenon-uniform openings may occur between the vanes, resulting inundesirable dynamic influences on the system of flow.

The main inconvenience of all these devices lies in the fact that therotating parts cannot be designed for speeds which would be essentiallylower than the maximum possible speed.

It is also known to utilize the centrifugal force for opening the bladesof the runner. With this arrangement, the runner blades are closed atincreased rotational speed of the turbine, independently'of the pressureoil from the pressure device. The connection between the closing and theopening spaces of the servomotor is realized through a centrifugaldistributor mounted in the head of the runner. At an increase of therotational speed of the turbine, the centrifugal dis-' tributor connectsthe said two spaces of the servomotor thereby rendering possible theopening of runner blades. The disadvantage of this arrangement lies inthe difficult adjustment of the centrifugal distributor because thewhole space of the turbine runner must be provided with drainingequipment for rendering possible the access to the centrifugaldistributor. Furthermore, thev centrifugal distributor cannot warrantthe opening of runner blades with a favourable time dependence but theopening changes permanently in accordance with variations of therotational speed, since the oil can flow only from the closing spaceinto the opening space.

It is the object of the present invention to remove these disadvantagesand to provide a safety device which will operate independently ofrotating parts and other auxiliary devices and will, in accordance withthe turbine speed, control the opening or closing of the runnerblades.

This object is attained according to the present invention by a safetydevice for preventing the excessive speeds of water turbines, equippedwith a runner with swivelling vanes moved by a sole servomotor connectedwith the oil supply and with the main distributor slide valve, safetydistributor valve is inserted between the oil supply and the maindistributor valve. In a particular embodiment an auxiliary distributorvalve is inserted on the constant-pressureside of the safety distributorvalve, the auxiliary distributor valve being further connected to thepressure-oil supply from the protecting organs of the turbine. Thesafety distributor valve is characterized in that it has a casing withpreferably six channels for connection of pipelines incoming from theoil supply or the servomotor, respectively, whereby the channels-arearranged in such a way that a rapid switch-over of the piston isobtained at increased turbine speed and so the main distributor valve istotally separated by closing the corresponding channels. Other featuresof the safety device according to the present invention will be evidentfrom the following description.

The invention is illustrated and described in detail with reference toaccompanying drawing which:

FIG. I a sectional view of the fundamental elements of the safetydevice,

FIG. 2 a longitudinal cross-section of the safety distributor valveaccording to the invention.

In FIGS. 1 and 2 the fundamental assemblies of the safety deviceaccording to the present invention are designated with the followingreference numbers: the turbine l, the main distributor slide valve 2 ofthe servomotor of the turbine guide wheel, the safety distributorvalve3, the auxiliary distributor valve 4 and the servomotor 5 with the oilsupply.

The turbine shown in FIG. 1 has a runner passage 11, over which andabove the helical channel the turbine guide wheel 12, is placed and,overlying it, the bearing of the runner 13, having the shaft 131. Therunner blades 132 are swivelled with the aid of servomotor 5. Referencenumber 14 designates the cover of the alternator, 15 the turbinedischarge pipe, 16 the cover of the oil supply 500. The servomotor 5 ofthe runner comprises a piston 51 built into a corresponding casing. Thespace above the piston where oil issupplied when the blades 132 have tobe opened is the opening space 52, the space under the piston where oilis supplied when the blades should be closed is the closing space 53.For opening the blades 132 oil is supplied into the opening space 52 andpressed out from the closing space 53, while for closing the blades, oilis supplied into the closing space 53 and pressed out of the openingspace 52. Along the axis of the piston there is machined a channel 531for supplying or discharging oil, or two channels 521 for supplying ordischarging oil, respectively, are connected with the space 52, wherebythe corresponding chambers in the cover 16 of the oil supply 500 bearthe-same reference numbers. The runner blades 132 are closed when thepiston 51 is lifted and the closing space 53 increases, while the runnerblades are opened when said piston lowers, reducing the closing space.The opening direction is marked by arrow 0, the closing direction byarrow 2. Closed runner blades have the plane of a blade forming asmaller angle with respect to plane perpendicular to the runner axis,opened runner blades have the plane of a blade forming a greater anglewith respect to said plane perpendicular to the runner axis, and thusthe blades in duce a braking effect.

The main distributor slide valve 2 of the servomotor of the turbinerunner comprises a casing 21 containing a movable piston rod 22 with thepistons 23, 24, and 25. The casing 21 has an opening 212 for theconnection with the opening 315 of the safety distributor valve 3.further an opening 213 for the connection with the opening 316 of thesafety distributor valve 3. On the opposite side of the casing there isan opening 214 for free discharge of oil from the upper part of thevalve into the collector, while the constant-pressure oil supply 215comes from the pressure device not shown in the drawing. The freedischarge of oil 216 from the lower part of valve 2 leads to thereservoir, while the connection 211 is connected to the not turbinegovernor not shown.

The safety distributor valve 3 comprises a casing 31 closed with anupper cover 38 and a lower cover 39, having within it six channels,which are correspondingly arranged along the valve axis. In the casingthere is moved a piston rod 32 with a three-part piston, having as partsthe upper piston 33, the central piston 34, and the lower piston 35. Inthe valve position shown, corresponding to the position for thenormaloperation of the set, immediately below the upper piston 33 there is achannel 315' with the opening 315 for the connection with the opening212 of the distributor slide valve 2, and underneath there is a channel311' with an opening 311 connected to the chamber or the channel 531 ofthe oil supply 500 and through it to the closing space 53 of theservomotor.

In the region of the central piston 34, a channel 313 is made, leadingthrough the opening 313 to the throttle 37. Underneath the piston 34there is a channel 316 with the opening 316 connected to the opening 213of the distributor slide valve, and further on, below the channel 316there is a channel 312' with the opening 312, connected to the chamberor channel 521, respectively, of the opening space 52 of the servomotor.Through the elements 213, 316, 316', 312', 312, S21

oil can be supplied from the distributor slide'valve 2 into the openingspace 52 of the servomotor and in this way provoke opening of the runnerblades, while through the elements 212, 315, 315', 311, 311, 53] oil canbe discharged from the closing space 53 of the ser- In the region of thelower piston 35, a channel 314' is provided which through opening 314facilitates a free discharge of oil from the safety valve 3, and thedrain from the throttle 37 is also connected to the correspondingdischarge pipe. The channel 314' is connected with the bore 351 of thelower piston 35, with the annular groove 354 and the space 357 under thepiston 35, so that oil can be drained from this space.

Finally, a control channel. 3l4".is provided in the lower part of thevalve, which,-through the bore 352, is connected with the space 353 ofthe piston 35 and during control it prevents oil from entering the space357 when the piston is moving downwards.

Besides the already described features the lower piston 35 has thefollowing additional characteristics:

It has the shape of a cylindrical body with a hole along the axis of thepiston rod, which subsequently will be named constant-pressure space353. A bore 351 leads from the upper end of said space into the controlchannel 314". A sleeve 36 is inserted in the lower part of said space353 and is fixedly connected to the lower cover 39 at its lower endwhile at its upper end the piston 35 can slide along it. The uppersurface of said sleeve has the reference number 36a. Along its axis thesleeve has a bore 361 for the supply of constantpressure oil, in itslower part a bulge 36b, and in the upper part a sealing edge 36c. In theregion of the upper part of sealing sleeve 36 which occupies the lowerpart of the space 353, an annular groove 354 is provided in the body ofthe piston, to which groove a connecting bore 351' is provided from thechannel 314' for a free oil discharge. The lower surface of the lowerpiston35 bears the reference number 35a, the bottom surface of space 353the number 353a, whereby a small widening of this surface with respectto the mean width of this space is not taken into account as it is madefor technologic reasons. The control edge 355 on the outer mantle of thelower piston 35 cooperates with an edge of casing 31 at the bottom ofthe control channel 314". The control edge on the inner side of thepiston at the bottom of the annular groove 354 bears reference number356, the space below the piston 35 number 357.

The auxiliary distributor valve 4 comprises a casing with a piston rodand the pistons 4a and 4b, the latter resting on a spring. Theconstant-pressure connection 41 leads from the annular groove 411 of thecasing into constant-pressure space 353 of the safety distributor valve3, on the opposite side a constant-pressure oil supply 42, coming fromthe pressure device enters the annular groove 421 of the casing. Thedischarge connection 43 is connected to the annular groove 431 of thecasing. Through this connection oil is discharged from constant-pressurespace 353 when valve 3 moves downwards. In this case oil is fed throughthe supply connection 44 from protection organs of the turbine and movesthe piston 4a so that connection 42 is closed, while piston 4b is movedagainst the force of the spring so far that the connection 353, 41, 411,431, 43, oil collector (not shown) is established.

The safety device according to the present invention operates inprinciple as follows:

In determining the torque of runner blades depending upon the rotationalspeed of the turbine, the analysis of several types of runner blades hasshown that oil pressure in the closing space of the servomotor of therunner varies according to the equation:

When, e.g., the maximum possible number of revolutions be n 3 n then themaximum oil pressure in the closing space equals p 9 C. The coefficientC contains the characteristics of blades and of their crank mechanism.It follows that at an increase of rotational speed of a turbine therunner blades can be opened independently of the pressure oil of thepressure device. It is necessary only to provide for the needed oildischarge from the closing space 53 of the servomotor of the runner intothe oil collector. With such an arrangement the runner blades can befully opened.

When the oil pressure in the closing space 53 of the servomotor of therunner attains the value corresponding to the increased turbing speed,also the force is increased which is needed to move the distributorvalve 3 downwards. As soon as the sealing edge 360 is opened and theedge 355 closed, the distributor valve is shifted by its entire stroke,due to the discharge of the lower space 357 having an equal pressure asspace 53. The oil from space 53 is drained out through the throttle 37and the blades are fully opened. When the servomotor piston 51 rests onthe bottom of the servomotor casing and ceases to press the oil, the oilpressure in space 336 is reduced and the oil pressure of space 353 liftsthe piston 33, 34, 35 again into its upper position. Therewith the fullopening of the blades is finished while the remaining control system isseparated and the operating conditions are reestablished.

If we wish to start fully opening the runner blades to reduce the speedat unloading or to switch over the safety distributor valve arbitrarily,without regard to increase of speed, oil can be discharged from spaces353 or 357 through the auxiliary distributor valve 4. In case ofincreased speed, pressure oil is supplied from protection organs of theturbine to the auxiliary distributor valve 4 through the connection 44so that the pistons 4a, 4b are shifted establishing the connection 353,41, 411, 431, 43. In this way oil is drained from the space 357 allowingthe closing of runner blades similarly as in the case of operationwithout an auxiliary distributor valve.

Now the particulars of operation of the safety device according to theinvention will be described.

When the rotational speed of the turbine is greater than the ratedspeed, pressure in the closing space 53 of the servomotor is increased.Through the channel 531 and the groove of the oil distributor, oil underincreased pressure passes through the opening 311, the channels 311 and315 and the channels 331 and 332 of the upper piston 33 into the space336 above the piston. In this space now there is the same pressure as inthe space 53. When the turbine speed rises the servomotor piston 51 ismoved downwards and oil pressure in space 53 increases and so does it inthe space 336 above the upper piston 33 of the safety valve. When thepressure on the surface 333 of this piston overcomes the force actingupwards on the surface 353a of the constant-pressure space 353, thepiston rod 32 with the three pistons is forced to move downwards. Inthis instant there is still the same pressure acting on surfaces 35awhich is the lower surface of the lower piston 35 and 353a of theconstant-pressure space because the connection between these two spacesstill exists 6 through the bore 352, the control channel 314", and pastthe control edge 355. When the piston rod moves downwards, the lowerpiston 35 opens the connection between its control edge 356 and thecontrol edge 36c of the sleeve 36 before it closes the way past thecontrol edge 355. Therefore, through the bore 351, channel 314' and theopening 3114 oil passes into the outlet before the connection past thecontrol edge 355 into the control channel 314" is closed. As the forceon surface 333 increases, the valve slides quickly downwards. Now,pressure is applied only to the small surface 353a of theconstant-pressure space. At this downward movement the moving speed issomewhat braked by the bulge 36b of the sleeve immediately beforeseating on the bottom. When the piston 35 comes into its lower position,the distributor slide valve is totally separated since the upper piston33 has closed the opening 315 connected with the opening 212 of thedistributor slide valve, and the sleeve 36 has closed the opening 316connected with the opening 213 of the same valve. At

the same time it is rendered possible to drain oil from the servomotorspace 53 through the channel 531, the opening 313, the channel 313, andthe throttle 37. As it has already been mentioned, it is the task of thethrottle 37 to regulate the draining speed of oil from the space 53below the piston of servomotor 5, therefore by choosing adequatedimensions of this throttlethe opening speed of runner blades can bedetermined.

, The hydraulic torque always tends to open the blades and to press theservomotor piston downwards, therefore up to now it has always been aproblem how to drain oil from said space. The servomotor piston, namely,moves slowly downwards until it seats on the bottom of the casing of theservomotor 5 and at this instant the pressure in this part of theservomotor drops to zero. Accordingly, the pressure zero is also in thespace 336 above the upper piston 33 of the safety valve 3. The pressureexerted on the small surface 353a of the constant-pressure space 353 nowsuffices for lifting the piston rod 32 with all three pistons up intothe operating position. Here it must be particularly noted that oil fromthe pressure device is not at all needed for opening the runner bladesbut only the torque of the runner blades, which at increased speed actsin the sense of opening, is utilized.

The speed regulation of the piston movement of the safety distributorvalve is rendered possible by an arrangement in the upper piston 33. Itsleft side contains a channel 331 for draining oil through a single-wayball valve 334. The right side contains a channel 332 which has athrottle 335 fitted next to the upper cover 38. When pressure is appliedto the upper side of the upper piston 33, the space is filled, the ballof the single-way valve 334 is lifted, and oil flows quickly primarilythrough the single-way valve 334 and also through the nozzle 335. Whenthe piston moves back into the working position, the oil contained abovethe upper piston 33 closes the ball valve 334 and can drain out onlyvery slowly through the nozzle 335.

The upper piston 33 has a threaded bore 381 which serves for thesupervision of oil pressure or of piston position of the safetydistributor valve and is closed by a locking screw 382.

Now there are to be described the details of the distributor valve 4.This distributor valve serves to switch over the safety valve 3 alreadyat low turbine speeds so that it is not necessary to wait that thepressure on the upper surface 335 of the upper piston 33 would increase,i.e., till the moment when the number of revolutions of the turbine hasincreased. Pressure oil is supplied from the pressure device of thegovernor through connection 44 pressing the piston 4a of the distributorvalve so far inwards thet the constant-pressure oil supply is closed andthe connection 43 opened so that oil pressure is removed from thesurface 353a of the safety valve through the annular groove 411 and theconnection 41. Since the safety valve moves downwards oil can go to theoutlet through the throttle 37.

The actuation of the auxiliary distributor valve 4 can be arranged,e.g., by a frequency relay and a magnet valve which switches over thedistributor valve at any desired increase of frequency.

The arrangement according to the present invention has considerableadvantages. At an increase of turbine speed determined in advance, thisdevice renders possi ble a reliable full opening of runner blades andconsequently a reduction of speed. For opening the blades thereby it isnot necessary to supply pressure oil into space 52 since the hydraulictorque itself. opens the blades, therewith forcing the servomotor pistonto be shifted downwards, only oil must be drained from the space 53.

A further advantage lies therein that the device may be inserted at anydesired place of the power plant, to-

tally separated from the turning parts of the turbine. lt can bemounted, dismantled, and adjusted without previous emptying of theturbine bay. The device operates fully independently of the turbinegovernor or other safety devices. Finally, the economic side is alsoimportant as the cost of the complete device amounts to approximatelyone per cent of theprice of the turbine governor. All other systems ofprotection do not offer an equivalent protection against the increase ofrotational turbine speed, but their price considerably exceeds the priceof the turbine governor. The complete arrangement does not operatestatically but astatically. It is started immediately when the speed isincreased to a given amount and it operates until the blades are fullyopened.

It remains, of course, in the frame of the invention when the safetydistributor valve is of a larger size in order to eliminate friction atcontrol and to prevent sticking on the edges of channelsand when it isdesigned otherwise, e.g., with the help of a sliding sleeve substitutingthe upper and middle piston and having correspondingly arrangedopenings. But such an embodiment must still take into account theconnection of this valve with the servomotor of the runner and thedistributor slide valve which is the object of the present invention andfor which protection is claimed.

What I claim is:

' 1. An hydraulic turbine comprising:

a runner;

a plurality of blades swivelable on said runner;

an hydraulic servomotor on said runner formed with a pair .of oppositelypressurizable chambers and a piston between said chambers, said pistonbeing operatively connected to said blades for varying inclinationthereof to control the speed of said runner;

an hydraulic-fluid source;

a servo-control valve connected to said source and having a pair ofports;

means forming respective flow paths connecting each of said ports with arespective chamber; and

safety-valve means removed from said runner and connected between saidservo-control valve and said servomotor, said safety-valve meansincluding:

valve-seat means formed on said valve member and normally effective toblock drainage of said compartme'nt but opening to permit such drainageupon the hydraulic biasing of said valve member toward said firstposition upon the development of an overspeed condition of said runnerto substantially instantaneously shift said valve member from saidsecond position into said first position and drain one of said chambersto enable said blades to swivel into an open condition.

2. The hydraulic turbine defined in claim 1 wherein I said valve memberhas upper, middle and lower piston formations axially spaced apartthereon, said upper and middle'formation being respectively interposablein respective passages upon displacement of said valve member from saidsecond position into said first position, said lower formation definingsaid compartment, said means and said housing including a tubular memberprojecting axially from one end of said housing and slideably receivedin said lower formation while communicating with said other valve, saidtubular member defining within said lower formation an axial space, saidvalve-seat means including cooperative edges on said tubular member andsaid lower formation separable upon displacement of said valve memberfrom said second position to said first position, said lower formationbeing formed with a bore communicating between said space and theexterior of said lower formation.

3. The hydraulic turbine defined in claim 2 wherein said upper piston isformed with a pair of axial bores, one of said bores being formed with acheck valve and the other of said bores being formed with a throttle.

4. The hydraulic turbine defined in claim 3 further comprising at leastone throttle for controlling the draining of said compartment and saidone of said chambers.

1. An hydraulic turbine comprising: a runner; a plurality of bladesswivelable on said runner; an hydraulic servomotor on said runner formedwith a pair of oppositely pressurizable chambers and a piston betweensaid chambers, said piston being operatively connected to said bladesfor varying inclination thereof to control the speed of said runner; anhydraulic-fluid source; a servo-control valve connected to said sourceand having a pair of ports; means forming respective flow pathsconnecting each of said ports with a respective chamber; andsafety-valve means removed from said runner and connected between saidservo-control valve and said servomotor, said safety-valve meansincluding: an elongated valve housing formed with a pair of axiallyspaced passages respectively forming part of said paths and traversed byhydraulic fluid passing between said servo-control valve and saidservomotor, a valve member axially displaceable in said housing andhaving a first axial position obstructing said passages and draining atleast one of said chambers and a second axial position in which saidpassages are substantially unobstructed. means in said housing definingwith said valve member a compartment hydraulically pressurizable to biassaid valve member from said first position into said second position,and valve-seat means formed on said valve member and normally effectiveto block drainage of said compartment but opening to permit suchdrainage upon the hydraulic biasing of said valve member toward saidfirst position upon the development of an overspeed condition of saidrunner to substantially instantaneously shift said valve member fromsaid second position into said first position and drain one of saidchambers to enable said blades to swivel into an open condition.
 2. Thehydraulic turbine defined in claim 1 wherein said valve member hasupper, middle and lower piston formations axially spaced apart thereon,said upper and middle formation being respectively interposable inrespective passages upon displacement of said valve member from saidsecond position into said first position, said lower formation definingsaid compartment, said means and said housing including a tubular memberprojecting axially from one end of said housing and slideably receivedin said lower formation while communicating with said other valve, saidtubular member defining within said lower formation an axial space, saidvalve-seat means including cooperative edges on said tubular member andsaid lower formation separable upon displacement of said valve memberfrom said second position to said first position, said lower formationbeing formed with a bore communicating between said space and theexterior of said lower formation.
 3. The hydraulic turbine defined inclaim 2 wherein said upper pistoN is formed with a pair of axial bores,one of said bores being formed with a check valve and the other of saidbores being formed with a throttle.
 4. The hydraulic turbine defined inclaim 3 further comprising at least one throttle for controlling thedraining of said compartment and said one of said chambers.